Modern turbofan aircraft engines include thrust reversers that selectively reverse the direction of an engine's annular fan flow for use in decelerating an aircraft after touchdown. One type of thrust reverser for a turbofan engine includes a cascade array mounted in a selectively closable outlet opening in an engine's fan air duct. The cascade array includes a plurality of spaced, cascading vanes that redirect fan air flow along the engine's annular fan duct from an aftward direction to an outward and forward direction when the thrust reverser is deployed. Examples of various cascade-type thrust reversers are described and shown in, for example, U.S. Pat. No. 5,309,711; U.S. Pat. No. 6,170,254; and U.S. Pat. No. 6,546,715; all assigned to Rohr, Inc.
Portions of a typical cascade-type thrust reverser 10 for a turbofan aircraft engine 5 are shown in FIGS. 1A-1E. As shown in FIG. 1A, the cascade thrust reverser 10 includes a translating sleeve 16 that forms an aft portion of a nacelle surrounding the engine's annular fan duct 13. The translating sleeve 16 is movably connected to the aft end of a stationary portion 12 of the nacelle. For normal aftward fan flow through the engine's fan duct 13, the translating sleeve 16 is positioned immediately behind the stationary portion 12 of the nacelle and confines the fan flow within the fan duct 13. As shown in FIGS. 1A-1C, when the thrust reverser 10 is deployed, the translating sleeve 16 is moved aftward, thus providing an outlet opening 15 between the stationary portion 12 and the forward end of the translating sleeve 16. The outlet opening 15 typically extends on either side of a supporting engine pylon 7, and around a substantial portion of the circumference of the engine 5, and permits fan flow to be discharged from the engine's annular fan duct 13 to provide reverse thrust for slowing a landed aircraft. As shown in FIG. 1C, a plurality of blocker doors 18 proximate the forward end of the translating sleeve 16 are deployed to block aftward fan flow within the annular fan duct 13, and to force the fan flow to exit the engine through the outlet opening 15.
As shown in FIGS. 1A and 1B, a cascade assembly 20 is disposed within the exit opening 15, and typically includes a plurality of circumferentially arranged cascade segments 28. As shown in FIG. 1C, the cascade segments 28 include pluralities of spaced vanes 25 configured to turn the exiting fan flow to an at least partially forward direction in order to provide reverse thrust. The vanes 25 typically are supported between a plurality of longitudinal support members 26. The aft ends of the cascade segments 28 are interconnected by an aft cascade ring 30 that ties the cascade segments 28 together, and stiffens the cascade assembly 20 against outward deflection. As shown in FIG. 1D, the aft end of each cascade segment can include an end flange 29, and can be connected to the aft cascade ring 30 by a plurality of removable fasteners 21.
In the embodiment shown in FIGS. 1C and 1D, the aft cascade ring 30 includes an outer portion 36 and an inner portion 34 that are each connected to opposed ends of a body portion 32 at right angles. The substantially Z-shaped cross-section of the cascade ring 30 provides the ring with substantial stiffness against bending and twisting, though all portions 32, 34 and 36 of the ring are relatively thin. As also shown in FIGS. 1C and 1D, an aft vane 27 in each cascade segment 28 defines the rearmost extent 11 of the exhaust plume as the redirected fan flow exits the outlet opening 15. As shown in FIG. 1D, the aft vane 27 is positioned forward of the aft cascade ring 30, and the aft cascade ring 30 is positioned behind the rearmost extent 11 of the exhaust plume by a distance “a”. Accordingly, the aft cascade ring 30 has no substantial or direct effect on turning the exiting fan flow as the flow passes through the exit opening 15.
Another configuration of a known aft cascade ring 60 is shown in FIG. 1E. In this arrangement, each cascade segment 58 includes a rearward extending flange 52 for connection to a forward extending flange 63 of aft cascade ring 60 with a plurality of removable fasteners 21. The aft cascade ring 60 generally includes a body portion 69 and opposed inner and outer portions 67, 65. Again, the cross-sectional shape of the ring 60 provides substantial stiffness, though the individual portions 63, 65, 67 and 69 of the ring 60 are relatively thin. As shown in FIG. 1E, the aft-most vane 57 is positioned forward of the ring 60, and the ring 60 is positioned behind the rearmost extent 11 of the exhaust plume by a substantial distance “b”. Accordingly, like the aft cascade ring 30 described above, the ring 60 has no substantial or direct effect on turning the exiting fan flow as the flow passes through the exit opening 15.
Though the aft cascade rings 30, 60 described above can be used to securely and rigidly connect the aft ends of thrust reverser cascade segments, they have some shortcomings. First, as discussed above, the aft cascade rings 30, 60 play no substantial or direct role in turning exiting fan flow, and thus are ancillary to the primary function of their cascade assemblies 20, 50. Second, because the aft cascade rings 30, 60 are positioned aft of the aft-most cascade vanes 27, 57, the aft cascade rings 30, 60 add to the overall length of the cascade assemblies 20, 50, as well as add extra weight to the cascades 20, 50 without directly contributing to their air-turning function. Accordingly, at least for these reasons, there is a need for an improved thrust reverser cascade assembly with an improved aft cascade ring that directly contributes to the air-turning function of the cascade assembly, as well as for its primary function of offering structural support for the aft end of the cascade array. This effectively reduces the overall length and weight of the cascade assembly.